U.S. patent number 7,417,779 [Application Number 11/066,834] was granted by the patent office on 2008-08-26 for single piece torsional hinged device with central spines and perimeter ridges to reduce flexing.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to John W. Orcutt.
United States Patent |
7,417,779 |
Orcutt |
August 26, 2008 |
Single piece torsional hinged device with central spines and
perimeter ridges to reduce flexing
Abstract
A torsional hinged device having an optical surface, such as a
mirror or refractive surface, formed from a single piece of silicon
with reduced flexing. In addition to central spines to prevent or
reduce flexing of the tips of the optical surface, the device may
also include perimeter ridges to further reduce or prevent flexing
as well as reduce warping of the edges of the optical surface. To
allow balancing of the device so that the center of mass of the
assembly is on the pivoting axis, a recess is formed in the back
portion to receive a permanent drive/sense magnet.
Inventors: |
Orcutt; John W. (Richardson,
TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
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Family
ID: |
34753886 |
Appl.
No.: |
11/066,834 |
Filed: |
February 24, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050225821 A1 |
Oct 13, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10681934 |
Oct 9, 2003 |
6956684 |
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10682015 |
Oct 9, 2003 |
6999215 |
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60556121 |
Mar 24, 2004 |
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60424915 |
Nov 8, 2002 |
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Current U.S.
Class: |
359/224.1;
359/198.1 |
Current CPC
Class: |
B81B
3/007 (20130101); G02B 26/0858 (20130101); G02B
26/085 (20130101); B81B 2201/042 (20130101) |
Current International
Class: |
G02B
26/08 (20060101) |
Field of
Search: |
;359/224 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Phan; James
Attorney, Agent or Firm: Kempler; William B. Brady, III; W.
James Telecky, Jr.; Frederick J.
Parent Case Text
This application claims the benefit of U.S. Provisional Application
No. 60/556,121, filed on Mar. 24, 2004; and is a
Continuation-In-Part of U.S. application Ser. No. 10/681,934 filed
on Oct. 9, 2003, now U.S. Pat. No. 6,956,684 which claims benefit
to Provisional Application No. 60/424,915, filed on Nov. 8, 2002;
and is a Continuation-In-Part of U.S. application Ser. No.
10/682,015 filed on Oct. 9, 2003, now U.S. Pat. No. 6,999,215 which
claims benefit to Provisional Application No. 60/424,915, filed on
Nov. 8, 2002. Each of these applications is hereby incorporated
herein by reference.
Claims
What is claimed is:
1. A single piece torsional hinged device comprising: a front
portion defining an optical surface with a perimeter edge, and
having a first dimension and a second dimension orthogonal to said
first dimension, said first dimension extending between first and
second ends of said optical surface; a back portion integral with
said front portion, said back portion including a center section
and first and second end sections, each of said first and second
end sections defining a central spine extending from said center
section along said first dimension; and a pair of torsional hinges
integrated with extending away from said center section and along a
pivotal axis, said pivotal axis parallel to said second
dimension.
2. The single piece torsional hinged device of claim 1 wherein said
first and second end sections of said back portion further comprise
a pair of perimeter ridges extending from said center section of
said back portion and along said perimeter edges of said front
portion toward said first and second ends.
3. The single piece torsional hinged device of claim 1 and further
comprising a permanent magnet mounted to said back portion.
4. The single piece torsional hinged device of claim 3 further
comprising a magnetic coil that interacts with said permanent
magnet.
5. The single piece torsional hinged device of claim 4 wherein said
permanent magnet and said coil provide rotational energy to said
torsional hinged device.
6. The single piece torsional hinged device of claim 5 wherein said
torsional hinged device oscillates at its resonant frequency.
7. The single piece torsional hinged device of claim 4 wherein said
permanent magnet and said coil operate as a sensing device.
8. The single piece torsional hinged device of claim 1 wherein at
least one of said pair of torsional hinges further defines an
enlarged area and further comprising a permanent magnet attached to
said enlarged area for imparting oscillating motion to said
torsional hinged device.
9. The single piece torsional hinged device of claim 8 and further
comprising at least one magnetic coil that interacts with said
permanent magnet attached to said at least one enlarged area.
10. The single piece torsional hinged device of claim 9 and further
comprising a sensing magnet mounted to the backside of said back
portion and a magnetic coil that interacts with said sensing
magnet.
11. The single piece torsional hinged device of claim 8 wherein
both torsional hinges of said pair of torsional hinges define
enlarged areas and wherein each enlarged area has a permanent
magnet attached thereto.
12. The single piece torsional hinged device of claim 11 wherein
one magnet on one of said enlarged areas is for imparting
oscillating motion and the magnet on another one of said enlarged
areas is a sensing magnet.
13. The single piece torsional hinged device of claim 11 wherein
both magnets on said enlarged areas are for imparting oscillating
motion.
14. The single piece torsional hinged device of claim 11 and
further comprising first and second magnetic coils that interact
with said permanent magnets on said enlarged areas.
15. The single piece torsional hinged device of claim 1 wherein
said center section of said back portion defines a recess and
further comprises a permanent magnet mounted in said recess.
16. The single piece torsional hinged device of claim 1 and further
comprising a piezoelectric drive unit to impart said oscillating
motion to said torsional hinged device.
17. The single piece torsional hinged device of claim 16 and
further comprising a permanent magnet mounted to the backside of
said back portion, and a magnetic coil that interacts with said
permanent magnet, said magnet and magnetic coil operating as a
sensing device.
18. The single piece torsional hinged device of claim 1 wherein
said optical surface is a reflective surface or mirror.
19. The single piece torsional hinged device of claim 1 wherein
said optical surface is a refractive surface.
20. The single piece torsional hinged device of claim 19 wherein
said refractive surface is a transparent lens.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application relates to the following co-pending and commonly
assigned patent applications: Ser. No. 11/054,926, filed Feb. 10,
2005, entitled A Multilayer Torsional Hinged Mirror With A Recessed
Drive/Sensing Permanent Magnet; and Ser. No. 11/055,392, filed Feb.
10, 2005, entitled A Torsional Hinged Mirror Assembly With Central
Spines And Perimeter Ridges To Reduce Flexing, which applications
are hereby incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to maintaining an optical surface
with reduced flexing during the operation of a torsional hinged
device such as a mirror, and more particularly to inexpensive one
piece torsional hinged optical devices and especially mirrors.
BACKGROUND
Pivoting or oscillating torsional hinged mirrors provide very
effective yet inexpensive replacements for spinning polygon shaped
mirrors in printers and some types of displays. As will be
appreciated by those skilled in the art, torsional hinged mirrors
may be MEMS type mirrors etched from a silicon substrate using
processes similar to those used in the manufacture of semiconductor
devices. Many torsional hinged mirrors provide a raster type scan
for printers and displays and operate at rotational speeds of about
3 KHz. However, as the demand for higher print speeds and better
resolution increases, flatness of the mirror reflective surface has
now become a much more serious problem. As the mirror continuously
flexes or bends back and forth during the continuous oscillations
about the axis, the greatest deformation is at the tip or ends of
the flexing mirror. Presently available mirrors have substantially
reduced this problem by the use of several bonded layers of
material such as silicon. Unfortunately, manufacturing a mirror
comprised of two or more layers significantly increases costs. In
addition, the greater rotational speeds and demand for thinner
mirrors, has also resulted in some flexing of the mirror around the
edges of the mirror during operation.
More specifically, referring to the prior art FIG. 5A, there is
illustrated a single piece torsional hinged device 10 such as a
mirror or other optical surface that oscillates on its torsional
hinges 12a and 12b about a pivoting axis 14. Although perhaps
exaggerated, the cross-sectional view of FIG. 5B illustrates how
the top half of an optical surface portion or mirror 16 of device
10 flexes during a complete pivoting cycle. This type of excessive
flexing is unacceptable, although some flexing can be tolerated for
many applications. As discussed above, the excessive flexing may be
solved by a multi-layer mirror or device. However, for many uses,
the multi-layer mirrors or devices are too expensive.
Therefore, it would be advantageous to provide an inexpensive
torsional hinged optical surface or mirror that has reduced
flexing. Other optical surfaces, such as refractive surfaces, would
also benefit from the teachings of this invention.
SUMMARY OF THE INVENTION
These and other problems are generally solved or circumvented, and
technical advantages are generally achieved, by preferred
embodiments of the present invention, which provide a single piece
torsional hinged device having reduced flexing. The single piece
device comprises a front portion that defines an optical surface,
such as a reflective surface or a refractive surface, with a
selected perimeter edge. A first dimension of the front portion
extends between first and second ends or tips. A second dimension
of the optical surface is orthogonal to the first dimension.
A back portion of the device is integrally formed with the front
portion and includes a center area and first and second end areas.
Each of the first and second end areas defines a central spine
extending from the center area along the first dimension and toward
the first and second tips of the front portion respectively. There
may also be included a pair of perimeter ridges that extend from
the center area of the back portion along the perimeter edge of the
front portion toward the first and second tips respectively.
According to a first embodiment of the invention, the front portion
and back portion comprise a single unitary or integral piece of
material, such as for example a silicon substrate. The central
spine may be formed by using typical MEMS semiconductor
manufacturing processes. The silicon material comprising the back
portion is etched so as to define the central spines. A second
embodiment similar to the first embodiment may further include
perimeter ridges also etched into the back portion of the single
piece of silicon.
The center area of the back portion also defines a pair of
torsional hinges that extend away from the center area and along a
pivot axis that is parallel to the second dimension. The torsional
hinges then terminate at first and second anchor members that are
attached to a support structure.
A permanent magnet that may function as a drive magnet or
alternately a sensing magnet may be mounted to the back portion of
the device. A magnetic coil that interacts with the permanent
magnet is positioned proximate the magnet.
According to another embodiment, one or both of the torsional
hinges may define an enlarged area. A permanent drive magnet is
then bonded to the enlarged area(s). If this arrangement is used, a
permanent magnet mounted to the back portion of the device would
typically be used as a sensing magnet to determine the rotational
position of the device. However, in an alternate embodiment, a
permanent magnet on one enlarged area may be used to impart
oscillating motion and the magnet on the other enlarged area may be
used as a sensing magnet.
According to still another embodiment of the invention, the center
area of the back portion of the device defines a recess for
receiving a drive/sensing permanent magnet. The permanent magnet is
mounted in the recess to provide pivotal motion to the complete
assembly, or to act as part of a circuit to sense and monitor the
pivotal motion of the device. It will also be appreciated that the
optical surface of the device may be a reflective surface, such as
a flat mirror or a mirror with a selected curvature. Alternately,
the optical surface may be a refractive surface such as a fresnel
or gradient lens or a transparent refractive lens.
The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter, which form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and specific embodiment disclosed may be
readily utilized as a basis for modifying or designing other
structures or processes for carrying out the same purposes of the
present invention. It should also be realized by those skilled in
the art that such equivalent constructions do not depart from the
spirit and scope of the invention as set forth in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the
advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawing, in
which:
FIG. 1 illustrates a single piece torsional hinged device according
to an embodiment of the present invention;
FIG. 2 is similar to the mirror device of FIG. 1 and further
illustrates perimeter ridge structures along the edges of the
optical surface portion;
FIG. 3 illustrates the use of a drive magnet mounted to an enlarged
area on at least one of the torsional hinges, and may be used with
both the embodiments of FIG. 1 or FIG. 2;
FIG. 4 illustrates another embodiment similar to FIGS. 1, 2, and 3
but further includes a recess defined in the back portion of the
center area for receiving a permanent drive/sensing magnet; and
FIG. 5A is a perspective view and FIG. 5B is a partial
cross-sectional view taken along line 5b-5b of FIG. 5A illustrating
the flexing problem of prior art mirror structures solved by the
present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The making and using of the presently preferred embodiments are
discussed in detail below. It should be appreciated, however, that
the present invention provides many applicable inventive concepts
that can be embodied in a wide variety of specific contexts. The
specific embodiments discussed are merely illustrative of specific
ways to make and use the invention, and do not limit the scope of
the invention.
Referring now to FIG. 1, there is shown a back view of a first
embodiment of the assembly 20 of the present invention having an
optical surface, such as for example a mirror. As shown, the device
22 is formed from a single piece of material such as silicon, and
comprises a front portion 24 defining an optical surface such as a
reflective surface or a refractive surface integral with a back
portion 26. A permanent magnet 28 is bonded to the back side 26b of
back portion 26. As will be described in more detail later,
permanent magnet 28 may be a drive magnet for imparting oscillating
rotation about a pivoting axis 30 to the assembly. In one
embodiment, the device assembly with the magnet oscillates at its
resonant frequency. Alternatively, permanent magnet 28 may be used
as a monitor or sensing magnet to provide information concerning
the pivotal motion of the device 22.
Further, permanent magnet 28 is preferably selected so that the
center of mass of the device 22, with the magnet attached, lies on
pivoting axis 30. The embodiment of FIG. 1 also includes a magnetic
coil 32 that interacts with permanent magnet 28 to provide the
rotational torque to the device 22. Alternately as discussed above,
the permanent magnet 28 may be a sensing magnet for providing
information about the movement of the device 22 due to changes in
magnetic flux as the position of the permanent magnet changes.
Referring again to FIG. 1, it is seen that the front portion 24 of
device 22 includes a selected thickness as indicated by double
arrows 34, and that back portion 26 includes central spines 36a and
36b. Although not necessary, the back portion 26b will typically
have a greater thickness than the front portion 24.
According to a second embodiment of the invention and as
illustrated in FIG. 2, there may also be included a pair of
perimeter ridges 38a and 38b at a first end of the device and
perimeter ridges 38c and 38d at the other end. As mentioned above,
the front portion 24 with the optical surface and the back portion
26 of the device 22 is comprised of a single or unitary piece of
silicon with the support spines 36a and 36b, and the perimeter
ridges 38a, 38b, 38c and 38d etched into the silicon of the back
portion 26. According to the embodiments of both FIGS. 1 and 2, the
front portion 24 of device 22 defines a front optical surface 40,
such as a mirror or refractive surface having a perimeter edge 42.
A first dimension 44 of the device 22 extends between a first end
or tip 46a and a second end or tip 46b (shown in FIGS. 1 and 2). A
second dimension 48 extends orthogonally to the first dimension,
and parallel to the pivoting axis 30. The back portion 26 of the
device 24 is formed to define a center portion 50, and the central
spines 36a and 36b extend from the center portion 50 parallel to
the first dimension 44 toward the first and second ends or tips 46a
and 46b as shown in FIG. 1. The perimeter ridges 38a-38d, shown in
FIG. 2 also extend from the center portion 50 and follow the
perimeter edge 42 of the device 22 toward the first and second
ends. The back portion 26 of the embodiments of both FIG. 1 and
FIG. 2 also includes a pair of torsional hinges 52a and 52b that
extend from the center section 50 along the pivoting axis 30.
Pivoting axis 30 is parallel to the second dimension 48 as
mentioned above. Also as shown in FIGS. 1 and 2 and as is discussed
above, permanent magnet 28 may be bonded to the backside 26b of
back portion 26 to provide rotational motion about the pivotal
axis. Alternately, the permanent magnet 28 may be used to provide
information about the pivotal movement of the device.
Referring to FIG. 3, there is shown another feature of the
invention that may be used with the embodiments of both FIG. 1 and
FIG. 2. As shown in FIG. 3, the device 22 further comprises an
enlarged area 54a that is formed as part of torsional hinge 52a. A
permanent magnet 56a may be bonded to the enlarged area 54a to
provide pivotal rotation to the device assembly in a manner know by
those skilled in the art. It should also be appreciated that a
similar enlarged area for supporting a second permanent magnet
could be formed as part of torsional hinge 52b. Referring again to
FIG. 3, it will be appreciated that the enlarged area 54a and
permanent magnet 56a may be used to provide motion to the device
22, while the permanent magnet 28 and sensing coil 32 provide
feedback information concerning the pivotal movement of the
assembly. Alternately, if both torsional hinges include enlarged
areas and permanent magnets, one magnet and associated coil can be
used to provide pivotal motion and the other magnet and associated
coil can be used as a sensing device to monitor the pivotal motion.
It should be appreciated, of course, that the invention covers
embodiments with and without the enlarged areas 54a and permanent
magnet 56a. Further, other drive techniques may be used to provide
rotational or pivotal motion to the assembly. For example, as will
be appreciated by those skilled in the art, a pair of piezoelectric
units may be used to input resonant motion to the assembly.
It should also be appreciated that the figures illustrating the
invention are not necessarily to scale, and may be intentionally
distorted to emphasize and help explain details of the
invention.
Referring now to FIG. 4, there is illustrated another embodiment of
the invention. FIG. 4 is similar to the embodiment of FIGS. 1, 2,
and 3, except that instead of a permanent magnet 28 being bonded to
the backside of back portion 26 as discussed above, a recess 60 is
formed in the back portion 26 for receiving the permanent magnet
28. The depth of the recess 60 as indicated by the double arrows 62
may be adjusted so that the center of mass of the combined mirror
device 22 and the permanent magnet 28 lies on the pivoting axis
30.
From the foregoing, it should be appreciated by those skilled in
the art that the use of central spines and perimeter edges, as
taught by the present invention, may be used advantageously to
reduce flexing of an oscillating mirror or other optical surfaces.
More specifically, the oscillating optical surface may be a flat
mirror or a mirror with a selected curvature. Alternately, the
optical surface could be a refractive optical surface such as a
gradient or fresnel (refractive and reflective) lens, or a
transparent refractive lens that passes light completely through
the optical structure.
Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims.
Moreover, the scope of the present application is not intended to
be limited to the particular embodiments of the mirror assembly
described in the specification. As one of ordinary skill in the art
will readily appreciate from the disclosure of the present
invention, mirror devices later to be developed, that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
mirror devices.
* * * * *